1. Field of the Invention
The present invention relates to a flat cathode ray tube, and more particularly, to a method for bonding a rail, which supports and fixes a shadow mask inside a flat cathode ray tube, in an inner surface of a panel.
2. Background of the Prior Art
In general, a cathode ray tube is used to embody an image of an image display substantially. Recently, various cathode may tubes, which can remove the distortion of image, minimize the reflection by the external light and maximize the visible range, have been designed and commonly used.
As shown in FIG. 1, the flat cathode ray tube includes a panel 1 coated with a fluorescent material at the inner surface, a funnel 5 adhered on the inner periphery of the panel 1. And, a neck portion 5a formed at an end portion of the funnel 5 and has a electron gun 6 inserted therein for emitting electron beam with three colors, i.e., red, green and black colors, and a deflection yoke 7 arranged on the outer surface of the neck portion 5a for deflecting the electron beam in the horizontal and vertical direction.
The panel 1 includes a safety glass 2 fixed to the front surface of the panel 1 by a resin and maintaining the radiation width of the cathode ray tube, a rail connecting member 3 fixed on the inner surface of the panel 1, and a shadow mask 4 mounted on the rail assembly 3 for selecting the color of the electron beam.
The rail assembly 3 within the flat cathode ray tube is a frame member comprised of two long rails, two short rails and four end caps, which are connected with each other. The rails and end caps are formed by a presswork. The rail assembly 3 is used for supporting and keeping the shadow mask 4 at a proper interval from the inner surface of the panel 1. The rail assembly 3 (hereinafter called xe2x80x9crailxe2x80x9d) is bonded in the panel 1 by the coagulation force of a frit glass 8 inside a furnace.
FIG. 2 is a flow chart of conventional bonding process of the rail and panel disclosed in U.S. Pat. No. 4,923,422. Referring to FIG. 2, the bonding process of the rail and the panel will be described in detail.
First, a predetermined amount of frit powder and vehicle are missed in a predetermined ratio to manufacture a frit glass 8, and then, the rail 3 is washed to remove impurities from the surface of the frit glass 8.
After that, the frit glass 8 in a melted state fills space formed at the rear portion of the rail 3, and after placed on the inner surface of the panel 1, the rail 3 is adhered to the panel 1 by the coagulation force of the frit glass 8 inside the furnace.
After the bonding process of the rail 3 and the panel 1 is finished, an upper surface 3a of the adhered rail 3 is ground to maintain a distance between the inner surface of the panel 1 and the shadow mask 4 at a certain interval. The assembly of the panel 1 and the rail 3 is washed to remove grind chips produced during the grinding process.
After a black matrix and a fluorescent film is an formed on the inner surface of the panel 1, the shadow mask 4, which is in an tensioned state, is arranged on the ground upper surface 3a of the rail 3, which is bonded to the panel 1. The shadow mask 4 is fixed on the upper surface 3a of the rail 3 by a welding method in order to prevent thermal expansion of the shadow mask 4 by the electron beam.
The conventional bonding process is a basic process, which bonds the rail 3 to the panel 1, of a series of processes for manufacturing the flat cathode ray tube, and however, there are several problems as follows.
(a) The bonding process is very complicated and it takes lots of time to perform the work. That is, the conventional bonding process includes a adhering step using a adhesive such as the frit glass 8. Since the frit glass 8 is contracted to an extent of about 20-30% during the adhering step, a grinding step is required to maintain the certain interval between the inner surface of the panel 1 and the shadow mask 4;
(b) The size of the panel 1 is increased unnecessarily. The rail 3 must be designed to have a certain height to keep the distance between the panel 1 and the shadow mask 4 and a width to maintain the bonding force for standing the tension of the shadow mask 4. However, in the prior art, since the height of the rail is increased by the frit glass 8 which is additionally mounted to the rail 3, larger moment is added to the bonded portion under a certain tension. Therefore, the width of the rail 3 is still more increased to increase the bonding force and the increased width of the tail 3 increases the size of the panel 1. Additionally, because the frit glass 8 is flowed outside from the rail 3 during the adhering step and then coagulated, it occupies an unnecessary area on the inner surface of the panel, thereby increasing the size of the panel 1; and
(c) The bonding process increases a badness rate and deteriorates the quality of the cathode ray tube.
As shown in FIG. 3, because the frit glass 8 used in the bonding process has a plurality of pores, foreign matters 9 such as fluorescent material used in a coating step intrudes into the pores and inserted into the bonded portions between the fit glass 8 and the panel 1 and between the frit glass 8 and the rail 3. Therefore, the foreign matters 9 fall off during a ventilating step for making the flat cathode ray tube in a vacuum condition, thereby resulting in stepping the shadow mask 4.
In addition, the frit glass 8 has residual gas therein generated during the bonding process, and the gas is discharged inside the cathode ray tube in a high vacuum condition, thereby polluting the cathode ray tube and deteriorating the quality thereof.
Accordingly, it is an object of the present invention to overcome the disadvantages in the prior art by providing a method for bonding a supporter of a shadow mask in a flat cathode ray tube, in which the supporter bonding process is simple and a work period of time is saved.
It is another object of the present invention to provide a method for bonding a supporter of a shadow mask in a flat cathode ray tube, in which the height of the supporter is increased at a minimum degree and the frit glass is not used on any area on the panel, so that the size of the panel can be reduced.
It is still another object of the present invention to providing a method for bonding a supporter of a shadow mask in a flat cathode ray tube, which excludes the intrusion of impurities and the production of gas, thereby improving the quality of the cathode ray tube.
The foregoing objects are accomplished in one embodiment by providing a method for bonding a supporter of a shadow mask in a flat cathode ray tube, the method comprising the steps of: washing a rail, which is a supporter of a shadow mask, and a panel of the flat cathode ray tube so as to remove impurities; arranging the rail at a certain position on the inner surface of the panel to place in an exact location; applying a predetermined pressure to the panel and the rail by a pressure device to stick closely; raising the temperature of the panel and the rail to a certain degree by a heating device; and applying a predetermined voltage to the panel and the rail so that the panel and the rail form a electrostatic field and are bonded by an electric bonding of the boundary surface.
The rail consists of iron(Fe) in a ratio of 60xcx9c75% by weight and chromium(Cr) in a ratio of 24xcx9c35% by weight, and the panel consists of sodium oxide(Na2O) and potassium oxide(K2O) with alkalinity in a ratio more than 6% by weight respectively.
It is preferable that the pressure applied to the panel and the rail during the bonding process is within a range of 1xcx9c10 kgf/cm2 and the temperature of the panel and the rail is within a range of 100xcx9c520 degree.
Furthermore, it is preferable that the voltage applied to the panel and the rail is within a range of 200xcx9c4000V.
The bonded surface between the panel and the rail consists of metallic oxide layers with a thickness less than 2 xcexcm, and the metallic oxide layer is comprised of at least one or of more ferric oxide, chronic oxide and manganese oxide.
In the meantime, preferably, the method for bonding the supporter of the shadow mask of the flat cathode ray tube further includes a step of forming a black film layer on the surface of the rail after the washing step.
The film layer forming step is either a step for oxidizing the rail at a certain temperature and gaseous state during a predetermined period of time or a step for depositing predetermined materials on the rail under the vacuum condition.
The method according to the present invention reduces the production cost of the cathode ray tube and improves the quality thereof.